As concerns grow over the global warming, we are required to come up with efficient technology to control generation of global-warming substances and to process them when these are generated. The perfluorinated compounds, which are discharged in the semiconductor industry only, are mainly used in the CVD and etching processes, and are very stable and non-toxic to human health. However, since it takes 1,000-10,000 years or longer to decompose, meaning a considerably long period of time of being remaining on earth, it is imperative to develop technologies to process and reduce the compounds.
Accordingly, countries gathered for the World Filtration Congress (WFC) 1999 and agreed to set the strict standards to reduce PFC emission. In particular, participants from semiconductor industries in Japan continued countrywide project to develop substitute gas for the perfluorinated compounds, and recover and process the same.
The perfluorinated compounds are generally processed by oxidation, plasma decomposition, chemical sorption, adsorption removal, low-temperature freezing process, or catalytic oxidation.
The oxidation is the process that decomposes the compound by burning with electric energy at high temperature, which is the most generally-used method. However, due to considerable electric energy consumption and need for a separate apparatus for treating byproducts after the compound decomposition, the overall systems becomes somewhat complicated.
The plasma decomposition is the method of decomposing compounds using plasma, which is very strong energy, and this method can advantageously decompose almost all the hardly-decomposable matters. However, the treatment is considerably difficult when there is a large amount of incoming gas, and the maintenance or repair is also relatively difficult due to the presence of powder which is generated during plasma decomposition.
The chemical sorption is a process that allows the perfluorinated compound to react with chemical sorbent. It provides advantage that the treatment is free of exhaust gas, because the byproduct generated after decomposition of perfluorinated compound reacts with the chemical sorbent. However, the method suffers economic problem, because it is necessary to periodically replace the sorbent to suffice relatively large sorbent consumption.
The catalytic oxidation is a process that allows decomposition of perfluorinated compound by catalyst at reduced reaction temperature with increased decomposition efficiency. While it uses similar principle as the oxidation, the method provides advantage of decreased oxidation temperature, and reduced use of energy because the oxidation occurs at low temperature. However, the method needs to periodically replace the catalyst, because the halogen compounds such as HF, F2 that are generated after the reaction rapidly deteriorate the catalytic performance. Accordingly, researchers have worked on various ways to resolve the above-mentioned problem, such as, for example, regenerating the catalyst, which turns inactive by the contact with the halogen compounds, back into original catalytic state, by contacting the inactive catalyst with water vapor, or forming film on the catalyst surface, etc.
JP Patent Publication Nos. 11-70332 and 10-46824 made suggestion to decompose perfluorinated compound by metal supported aluminum oxide catalyst, which is prepared by supporting one or more of transition metals such as Zn, Ni, Ti, or Fe on alumina using precursors of metal complex, and U.S. Pat. Nos. 6,023,007 and 6,162,957 propose the use of a variety of metal phosphate catalysts for the decomposition of perfluorinated compounds. However, it requires rather complicated method to prepare aluminum phosphate in a form of multi-component complex oxide to which metal component is separately added, not to mention economic disadvantage and uncertainty as to whether it can be used for a long period of time. Accordingly, further improvements are required to increase catalyst durability and economy.
The present inventors have been able to prepare a catalyst for decomposing perfluorinated compound, which can completely decompose the perfluorinated compound containing acidic halogen compounds exhausted in semiconductor fabrication or LCD fabrication process, and which has high durability and thus can maintain catalytic activity for a long period of time, and thus completed the present invention.